Sequence
Stratifigraphic
Analysis
of Stratigraphic Oil
Traps in the West Siberian Neocomian
Oleg M. Mkrtchyan and John M. Armentrout
Large depositional oil traps (Priob, Sugmut, etc.) have been discovered in
the West Siberian Neocomian. Sequence
stratigraphic
analysis
of
well
logs and
seismic reflection profiles demonstrate that reservoirs of these fields
represent sands deposited during lowstand, transgressive and highstand phases of
relative sea level cycles. Transgressions and regressior advanced in regional
longitudinal and local latitudinal directions. The regional longitudinal pattern
is dominated by westward prograding clinoforms formed as the sediment supply
exceeded the accommodation space. Lock northward and northwestward prograding
complexes appear to be controlle by local basin-floor topography. In each
systems tract, the coastal zones were landward from the shelf-breaks resulting
in domina ce of marine facies each depositional shelf-edge.
Lowstand systems tracts are represented on the upper slope by prograding wedges with thin shelfal equivalents or correlative unconformities Sands deposited in these lowstand regressive facies comprise the main reservoir at Sugmut and a subordinate reservoir at Priob. Transgressive systems tracts are dominantly shale but in the Priob field one early transgressive parasequence sand contains an oil accumulation where immediately overlies a highstand shelf sand. Highstand systems tracts are represented by regional sheets over the shelf and by thick progradational complexes over the upper slope. Most of the sands occur within the late highstand parasequences and are difficult to correlate due to channel incision. Most Priob field reserves occur in the late highstand parasequences.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California